Process for treating hydrocarbons



Jan. 10, 1939. A. H. Boum-BEE PROCESS FOR TREATINC HYDROCARBONS Filed July 20, 1936 Patented Jan. 10, 192.59

umTrzoI STATES PROCESS FOB TREATING HYDBOCABBONS Arthur Hallam ncuitbce, Martinez, cant., mimor to Shell Development Company, San Francisco, Calii., a corporation of Delaware Application .lilly 20, 1936, Serial N0. 91,490 6 Claims. (Cl. 19E-10) i This invention relates to the production of aromatic and oleiinic hydrocarbons and hydrogen from mineral oils containing substantial amounts of naphthenic hydrocarbons and is particularly concerned with a new combination oi treating steps for producing high yields of valuable products.

Certain mineral crude oils, as California, Venezuela, Gulf Coastal, Columbian, etc. crudes 10 or distillates and/or solvent ramnates therefrom may contain besides aliphatic and aromatic hydrocarbons substantial amounts of naphthenes. Certain fractions, produced fromcrudes oithis type, for instance light or middle oils such as naphtha, kerosene, gas oil, etc. which have a high naphthene content, may be of relatively little value. For example, a gasoline distillate produced from a California crudemay have been stripped of its aromatic hydrocarbons which are used in the manufacture cr solvents. The remaining distillate in spite of its high content of naphthenes, having a low octane number and poor solvent quality, is generally quite undesirable. n It is the purpose of my invention to treat such oils in a manner so that they are converted t almost entirely to hydrogen, aromatic hydrocarbons, and low-boiling oleiines. Oleflnes produced in my process may be used to alkylate the aromatics or may be polymerized to gasoline,

lubricating ,oil or rubber-like polymers; undesirable polymer fractions may be separated, if

desired, and be depolymerized to olenes, the

latter being returned for repolymerization to more desirable polymers; the hydrogen or part of it may be utilized to hydrogenate suitable polymers, thereby stabilizing them and in the case of gasoline raising its antiknock value; and the aromatic hydrocarbons may be used as gasoline,

tractor fuel, solvents, or as starting material for the manufacture of av large variety of derivatives including lubricating oils, dyes, explosives, pharmaceuticals, etc.

My process comprises catalytically dehydrogenating a suitable naphthenic oil under conditions to dehydrogenate the naphthenes only,

thereby converting them to aromatic hydrocarbons and to leave aliphatic hydrocarbons substantially intact, separating the hydrogen so produced, subjecting the remaining oil to a cracking process to convert as large as possible a portion of the aliphatic hydrocarbons to lower boiling olenesand parailins, and separating the 'resulting cracked mixture to produce a relatively heavy aromatic fraction, a lighter aliphatic fractionK containing a substantial proportion of oleilnes, and a tar.

Catalytic dehydrogenation of hydrocarbon oils containing naphthenes and aliphatic hydrocarbons to produce aromatic hydrocarbons is known. 5 As catalysts may be employed, for example, metals such as silver, copper, iron, nickel, cobalt, aluminum or alloys thereof; or suliides or oxides of iron, nickel, cobalt, zinc, cadmium, aluminum, lead, bismuth, tin, vanadium, etc. Particularly 10 active are catalysts consisting of or containing oxides or suldes of the metals of the sixth group of the periodic system, namely of chromium, molybdenum, tungsten, uranium, selenium, tellurium, and polonium. Suldes, being 15 in general more resistant to catalyst poisoning than oxides or other types of compounds, are preferred. The catalysts may be used alone or in admixture with each other and deposited on solid carriers if desired. As carriers silica, var- 20 ious silicates such as pumice, clay, brick, un, glazed tile, asbestos, or porous carbon such as charcoal or metallurgical coke may be used.

Effective dehydrogenation temperatures vary considerably with the activity of the catalyst, 25 the more effective catalysts being active at temperatures between aboutf200 to 500 C. while the less activecatalysts may require temperatures between 500 and '700 C. To avoid cracking of the aliphatic hydrocarbons in the dehydro- 30 genation zone with consequent formation oi.' fixed hydrocarbon gases, such as methane, and of olefines which are undesirable in this step,

I usually select catalysts which are active below about 500 C. Oleiines, if allowed to form,'tend 35 to gum up the catalyst and render it inactive, while methane and the like contaminate the hydrogen, making it less valuable. I

The activity of many of the catalysts may be greatly prolonged by the presence of from, about 40 30 to 80 cubic feet reduced to normal of hydrogen per gallon of liquid oil to be dehydrogenated.

If dehydrogenation is carried out inthe vapor phase the hydrogen partial pressure in the vapors before dehydrogenation may advantageous- 45 1y range from about 30 to 80% of the total. pressure. Hydrogen produced in the dehydrogenation may be used by simply recirculating a portion thereof through the dehydrogenating zone. Instead of hydrogen, a gas containing hydrogen 50 may be used, if desired. oxidizing gases such as air, carbon dioxide, etc. should, however, be excluded.

The eilect of the hydrogen seems to be that oi' selectively suppressing dehydrogenaticn or 55 paramnic hydrocarbons to olefines. Olenes, as pointed out, tend to polymerize and gum up the catalyst. The presence of oxidizing gases apparently has the opposite effect, the result being olene formation and a reduction of the life of the catalyst.

Dehydrogenation may be carried out in the liquid or the vapor phase, depending upon the operating temperatures involved and the boiling range of the fresh feed. In general, I prefer vapor phase dehydrogenation, as it seems to be more eicient, and the .catalysts have longer lives. Pressures of the order of about 10 to 100 pounds per square inch were found to give good results.

Since it is the aim selectively to dehydrogenate naphthenes without substantially cracking parailins, it is obvious that if dehydrogenation temperatures are employed which are above the incipient cracking temperatures of the paraifins contained in the oil under treatment, the time allowed for the dehydrogenation must be suiliciently short, so as to prevent substantial cracking. 'I'he rates of cracldng for paraihns for various boiling ranges over a wide temperature range are known aproximately (Geniesse and Reuter, Ind. Eng. Chem. 1932, 24, page 219) and It is usually a question of economy as to'howY far paramns may be cracked in the dehydrogenation step. 'Ihe maximum allowable per cent cracking may vary within fairly wide limits but in most instances should be kept below about and preferably below about 2%.

Incipient cracking temperatures for normally liquid paraffin hydrocarbons are believed to lie between about the limits of 375 to 415 C., high boiling hydrocarbons generally having lower incipient cracking temperatures than lower boiling hydrocarbons.

One of the objects of my process is to produce aromatic hydrocarbons of a high degree of purity from mineral oils. The degree of purity which can be achieved by dehydrogenation alone depends on the concentration of the naphthenes in the initial material. Hydrocarbon oils, however, as produced commercially never consist altogether'of naphthenes, but contain varying amounts, usually 50% or more of aliphatic and aromatic hydrocarbons. For instance, California gasolines have been found to contain 35 to 45% naphthenes, while lVIid-Continent gasolines contain about 15 to 30%. Since the aromatic hydrocarbons resulting from dehydrogenation of naphthenes boil at about the same temperatures, it is diiflcult to separate by distillation such aromatic and unchanged naphthenes and aliphatic hydrocarbons contained in the products of dehydrogenation. To facilitate the concentration of aromatics by separating non-aromatics therefrom, I convert aliphatic hydrocarbons and unchanged naphthenes to lower boiling oleiines, by subjecting the dehydrogenated mixture to a non-catalytic cracking process without first separating aliphatic and aromatic hydrocarbons from each other. In this cracking step conditions are maintained. so that as large a portion aspossible of the non-aromatic hydrocarbons-is converted to lower boiling products, while aromatic hydrocarbons remain substantially unchanged, except for the possible loss of some alkyl side chains and a small amount of condensation to higher boiling poly-aromatic compounds such as pyrene, chrysene, or homologues, etc. The cracking is advantageously carried out at an effective cracking temperature of the order of 500 to 750 C. and preferably in the vapor phase at relatively low pressures, for instance below about 200 pounds per square inch, although pressures up to 1500 pounds may be used. The time of exposure to cracking temperatures is measured by the cracking per pass of the aliphatic hydrocarbons, cracking per pass being herein defined as the percent of aliphatic hydrocarbons converted to compounds boiling without, i. e. below or above, the boiling range of the aromatic fraction, which boiling range is usually substantially identical with that of the initial oil. Since during the cracking operation a certain amount of polymerization of olenes t0 polymers which may boil within the original boiling range is unavoidable, it is advantageous to use in my process relatively narrow fractions, because there will be less chance for the formation of polymers which boil within the boiling range of the original fraction. Hence the cracking per pass, under otherwise identical'conditions, must be greater for a relatively narrow original fraction than for a wider one. To realize the fullest advantage of my invention I therefore prefer to use, as initial materlal, fractions which have an A. S. T. M. boiling range of not more than about 50 C.

It is of some importance that in the cracking step the oil be heated from incipient cracking temperature to the effective cracking temperature in the shortest time possible and that at the end of the cracking reaction the cracked mixture -be shock chilled. Slow heating to the effective cracking temperature and failure to shock chill may cause polymerization of olenes to tar or to non-aromatic compounds which may boil within the boiling range of the aromatic fraction. Low boiling olefines being desired in my process for the manufacture of valuable synthetic products, this premature polymerization during the cracking operation should be avoided.

vDepending upon the type of olefines desired, the effective cracking temperature may vary -within the limits indicated above, higher temperatures in general tending to produce lower boiling oleflnes.

The cracked mixture produced in the cracking step is usually fractionated to separate a fraction having approximately the boiling range of the original oil consisting predominantly of aromatic hydrocarbons, a lighter fraction comprising oleflnes and parafiins, and a tar fraction. The tar is withdrawn and may be used as fuel, road oil, etc. The aromatic fraction may be used as solvent or as blending agent for gasoline or tractor fuel, or it may be refractionated and/or refined in various ways so that pure compounds, such as benzene, naphthalene, anthracene or their homologues such as alkyl derivatives may be prepared therefrom.

In an alternative procedure the cracked mixture is freed from tar and excessively volatile components such as methane, ethane, etc. by distillation, and the resulting distillate, which may or may not contain normally gaseous components, is subjected to a selective solvent extraction under conditions to separate essentially parafiins and naphthenes from aromatics and olenes. The paralni'c fraction is preferably returned to the non-catalytic cracking zone and the aromatics and olenes fraction may be further separated by distillation and/or solvent extraction, or the mixture may be treated with a condensing reagent such as phosphorous pentoxide, phosphoric acid,

' sulfuric acid, aluminum chloride, etc. to react the olenes and aromatics with each other, thereby producing alkylated aromatics suitable for antiknock gasoline, lubricating oils, poir point depressors, etc.

If the distillation of the cracked mixture is carried out in accordance with the usual procedure, the fraction comprising oleflnes is further fractionated to produce a light gas consisting essentially of ethane and lighter, which is discarded, a heavier normally gaseous fraction consisting mainly of 3 to 5 carbon hydrocarbons, and a normally liquid non-aromatic fraction comprising the heavier than pentane hydrocarbons; if desired, part or all of the five carbon hydrocarbons may be combined with the normallyV liquid fraction. The 3 to 5 carbon fraction is subjected to a polymerization to produce any desired polymer.

, For instance, it may be treated with phosphoric acid or the like to produce dipolymers suitable for gasoline, or with aluminum chloride to produce lubricating oils, or with boron fluoride to produce rubber-like polymers suitable for blending with lubricating oils. These polymers may be fractionated and be stabilized by hydrogenation, using hydrogen produced in the dehydrogenation step.

The heavier normally liquid non-aromatic fraction containing a considerable proportion of olenes may be returned to the non-catalytic cracking zone if desired. Due to the danger of converting the oleflnes in the cracking zone to polymers which may boil within the boiling range of the aromatic fraction, I prefer, however, to make use of one of two alternative vmethods for further cracking this fraction. I may subject the entire fraction to a catalytic vapor phase cracking process; or I may extract the fraction by selective solvent extraction under conditions to separate olenes from parafns or treat it in some other manner to separate saturated from unsaturated hydrocarbons, returning the parafns to the non-catalytic cracking zone and cracking the olenes catalytically.

At suitable elevated temperatures and in the presence of certain catalysts, oleiines break down to lower boiling hydrocarbons more readily than do parains. By maintaining relatively mild cracking conditions, olenes may be cracked or depolymerized to lower boiling olefnes without being substantially polymerized, while parafns remain largely unchanged. By a subsequent fractional distillation the lower boiling oleines` may then be separated from unchanged parailins, the latter being returned to the non-catalytic cracking treatment, while the 3 to 5 carbon oleiines fraction is combined with a similar fraction produced in the non-catalytic cracking treatment, the combination to be polymer-ized.

Products of polymerization usually are mixtures of more or less desirable polymers. Heretofore undesirable polymers constituted a loss. In my process, however, I return undesirable polymer fractions, after separating them by distillation, fractional extraction, etc. to the catalytic cracking treatment where they are depolymerized `to low boiling olenes, the latter then being'again polymerized to polymers, at least a portion of which is of the desirable type. 1n this manner I substantially increase the yield of the desirable polymers. f

Since my process is not concerned with theY manufacture of any particular polymers, reference is made to the prior art with respect to what polymers4 are deemed desirable or undeslr able. For instance, if it is attempted to produce gasoline by polymerization, polymers boiling within the gasoline boiling range are desirable, while higher boiling polymers are obviously undesirable; or if lubricating oils are to be produced,

polymers of a lubricating viscosity are desirable, while less viscous polymers are undesirable.

For cracking catalysts a large variety of substances may be used, for instance acidic oxides.

peratures between about 300 to 600 C. are usually suitable. Pressures may vary from substantially atmospheric to about 200 pounds per square inch, low pressures normally being conducive to the formation of olei'lnes. For instance when passing a mixture of duodecane and duodecylene over a calcined catalyst comprising phosphoric acid deposited on silica at a space velocity of one liquid volume of mixture per volume of catalyst per hour at 350 C. and substantially atmospheric pressure, a predominating portion of the olenes was broken down to Ca-Cs hydrocarbons, while the paraiins remained largely unchanged.

The aforementioned extraction of the nonaromatic fraction comprising normally liquid hydrocarbons may be carried out with any of the known selective solvents which are capable of separating parafiins from olenes, such as liquid sulfur dioxide, dichlor ethyl ether, furfural, nitrobenaene, phenol, cresilic acids, acrylic aldehyde, Croton aldehyde, etc. Conditions of extraction should be chosen so that the raifinate, which returns to the non-catalytic cracking` zone,

is substantially free from oleiines for reasons desired, to yield an unvaporized heavy fraction,` 'i which is discarded through bottom line 3, and a vapor fraction. The latter passes through vapor line 4 to heating coil 5 in furnace 6, where it is heated to an eiective dehydrogenation temperature between about 200 and 500 C. It then proceeds through line 6 to dehydrogenator 7. The dehydrogenator contains a suitable dehydrogenation catalyst of the type hereinbefore described. A total pressure of about 10 to 100 pounds per square inch may be maintained in the dehydrogenator, about 30 to 80% of which may be hydrogen partial pressure. Under these conditions the naphthenes in the vapors are dehydrogenated to aromatic hydrocarbons while paraflinic hydrocarbons remain substantially unaffected, and olenes, if present, tend to be converted to parafiins. The dehydrogenated vapors are condensed in condenser 8 situated in line 9, and the condensate so produced is separated from hydrogen ln separator I0. Blower II in line I2 picks up the hydrogen and returns a portion thereof through line I3 backto evaporator 2, while the remaining hydrogen is disposed of through line I4.

The condensate from separator I is forced by pump I5 in line I6 through heating coil I1 in furnace 6, through transfer line I8 to evaporator I 9 in which all but a residue boiling substantially above the boiling range of the original oll fraction passing through the dehydrogenator is vaporized under superatmospheric pressure. The residue, which is of tarry nature, is withdrawn through line 20 and discarded through line 2|.

The vapors, consisting essentially of aromatic and parailinic hydrocarbons, are allowed to expand through release valve 22 in line 23 to effect vaporization of entrained liquid. The resulting dry vapors are heated in coil 24 located in cracking furnace 25 to an effective non-catalytic cracking temperature between about 500 and '150 C. In the flrst part of the coil the vapors may be heated relatively gently to an incipient cracking temperature of the order of about 450 C'., and in the second part of the'coil they are quickly heated from the incipient cracking temperature to the effective cracking temperature, at which point they are held for the necessary length of time to effect the desired cracking of the paraffins, which time, depending upon the exact effective temperature, may vary from less than a second to about 60 seconds. At the end of the cracking period the vapors are quenched with a suitable quenching medium, such as water, or hydrocarbons, preferably boiling below the boiling range of the aromatic hydrocarbons contained in the cracked vapors such as pentanes or a substantially parafnic recycle stock, etc. The

quenching fluid is introduced through line 26 into' transfer line 21 through which cracked vapors are conveyed to a fractionating system shown as fractionator 28.

This fractionating system may comprise several fractionating columns, absorber, stabilizer, rectifier, circulating system for absorption oil, etc. Normally I separate five fractions from fractionator 28: a heavy tar fraction boiling above the boiling range of thearomatic fraction, the tar being discarded through line 2|; an aromatic fraction, usually boiling approximately Within the boiling range of the vapor fraction passing through dehydrogenator 1; an aliphatic fraction consisting essentially of olefines and parains boiling below the aromatic fraction comprising pentane and/or heavier hydrocarbons; a 3 to 5 carbon hydrocarbon fraction including olefines; and a waste gas fraction comprising ethane and lighter gases which gas goes through line 45 to a gas plant not shown. If desired the aromatic fractions and thepentane and/or heavier fraction may be combined, particularly if the fractionation is followed by a selective solvent extraction to separate aromatic from non-aromatic hydrocarbons as will be described.

The aromatic fraction may be conducted through line 29- and cooler 30 to storage tank 3l.

Or it may be directed through lines 29 and 32 to fractionator 33 to be separated by fractional distillation into any desired number of fractions having high concentrations of aromatic hydrocarbons. Such fractions are indicated in the drawing as light, medium, and heavy aromatic fractions, which are taken from fractionator 33 through lines 34, 35, and 36, coolers 31, 38, and 39, and run into run-down tank's 40, 4I, and 42 respectively.

If it is desired to produce aromatic fractions substantially free from non-aromatic components,

the aromatic fraction produced in fractionating system 2B may be conveyed through line 29' to extraction unit 43, in which non-aromatic impuritl'es are removed as rainate, while the aromatic extract goes through lines 44 and 29 to storage as hereinbefore described. The raffinate may be conveyed through lines 43, 62, and 63, pump I5 in line I6, etc. to the non-catalytic cracking unit, or disposed of in other ways as hereinafter described.

The 3 and 5 carbon hydrocarbon fraction produced in fractionating system 23 proceeds through lines 46 and 41 to polymerizer 48 which is charged a suitable polymerizing catalyst as hereinbefore described. Olenes contained in this fraction are polymerized. The resulting mixture is transferred through line 49 to fractionator 50, where the polymers are separated from the unreacted portion, the'latter going through lines 50 and 23 to the non-catalytic cracking unit. The polymers may be fractionated to separate desirable from undesirable polymers, the undesirable polymers returning through line 5I to the catalytic cracking unit to be depolymerized, while the desirable polymers enter hydrogenator 53 through line 52 together with an amount of hydrogen from line 55 and scrubber 54, which scrubber serves to remove sulfur compounds, particularly hydrogen sulilde, and other acidic substances, e. g. arsenic oxides, said amount being sufficient substantially to saturate the polymers. If desired all of the polymers may go through lines 52' and 52 to the hydrogenator 53. Hydrogen in line 55 in excess of that required to saturate the polymers is conducted through line 55' to storage. Hydrogenated polymers proceed through cooler 56 ln line 51 to separator 58 for the separation of unreacted hydrogen and then pass through line 59 to tank 60. Unreacted hydrogen is withdrawn through line 6I.

A portion or the Whole of the non-aromatic pentane and heavier fraction produced in fractionating system 28 together with the raffinate from extraction unit 43 and line 43 may be continually returned through lines 62, 63, and I6, pump I5, coil I1, line I8, evaporator I9, and line 23 to cracking coil 24 for recracking. For reasons hereinbefore discussed I prefer, however, to conduct at least a major portion of this fraction through lines 62, 64 togethenwith the raffinate from extraction unit 43 to the aforementioned catalytic cracking system, which comprises coil 65 in furnace 66, transfer line 61, and catalytic cracking chamber 68. In coil 65, the fraction is vaporized and heated to the necessary cracking temperature which may vary from about 300 to 600 C., depending upon the type of catalyst used. The heated vapors are then passed over the catalyst at a rate to effect substantial conversion of the olenes, while leaving the paraiilns largely unchanged and to form a substantial amount of 3 to 5 carbon olenes. The cracked vapors are introduced through line 69 into a fractionating system shown as iractionator 10, where they are fractionated to produce: a waste gas'fractlon consisting essentially of ethane and lighter which is discarded through lines 1I and 45; a 3 to 5 carbon fraction which goes through lines I2 and 41 to polymerizer 48; a pentane and heavier traction comprising largely parailins which is preferably returned through lines 13, 14,53, and I6, pump I5, etc. to the non-catalytic cracking system, or a portion of which may go through lines 13, 15, pump 16 in lines 16 and coil 65 tothe catalytic'cracklng chamber 68 if desired; and a tar fraction which is Withdrawn through tar line 11.

An alternate method of handling the pentane and heavier fraction produced in the fractionating systems 28 and 10 is to conduct them together with the raffinate from extraction unit 43 through lines 62, 18, and 13, 19, 18, respectively to a solvent extraction unit 80, where oleflnes are separated from parailinaolenes being pumped by pump 16 in line 1B to the catalytic cracking unit, and paraiiins going through lines 8i, 14, 63, I6, pump i5,-etc. to the non-catalytic cracking system. In this last manner the maximum amount of 3 to 5 carbon olenes for producing polymers which are especially. valuable for the manufacture of high antiknock gasoline and the like is obtained, with the least contamination of the aromatic fraction, the least amount of gas and tar losses, and the least amount of coking difficulties.

It shall be understood that' the particular flow diagram hereinbefore described is merely illustrative and that modiilcations of the various units such as the dehydrogenation unit, the cracking units, the fractionating units, the extracting units, etc. as known in the art but not shown in the diagram are Within the spirit of this invention. For instance the catalytic polymerization unit may be replaced-by non-catalytic thermal polymerization unit, or by a combination of catalytic and non-catalytic units as described in my co-pending application, Serial No. 86,122, filed June 19, 1936, and the unreacted 'hydrocarbons issuing from the polymerizer, in-

stead of returning to the non-catalytic cracking zone or zones just` mentioned, may be discarded or disposed of in some other suitable manner. Or the aromatic fraction prior to refractionation in fractionator 33 may be subjected to a rening treatment for instance by treatment with various chemicals such as sulfuric acid, alkali hydroxide, clay, etc. to remove sulfur compounds or to improve color and gum stability, odor, and so forth.

I claim as my invention:A

1. The process for treating a hydrocarbon distillate containing naphthenesv and parafiins comprising contacting said distillate oil with a dehydrogenating catalyst at an elevated temperature under time and pressureiconditions selectively to dehydrogenate said naphthenes Without substantially cracking said distillate and without substantially converting parains to lng range of the original distillate from said light olennes.

2. The process for treating a hydrocarbon distillate containing naphthenes and paraillns-comprising contacting said distillate oil with a dehydrogenating catalyst at `an elevated temperature under time and pressure conditions selectively to dehydrogenate said naphthenes without substantially cracking said distillate and without substantially converting paraiiins to olenes thereby converting naphthenes to aromatics and liberating hydrogen. separating the liberated hydrogen i'rom the resultant mixture of aromatics and paraiilns, subjecting said mixture to a noncatalytic vapor-phase cracking treatment under conditions to convert a major portion of the paraiiins into light olenes, including olenes of c and less carbon atoms, said light olenes bolling below the original boiling range of the distillate, without substantially changing the nuclei of the aromatics, fractionally distilling the cracked mixture to separate therefrom: an olefinic Ifraction comprising hydrocarbons with less-,than 6 carbon atoms, a tar-free aromatic fraction having substantially a boiling range within that of the original oil, and an intermediate substantially non-aromatic fraction comprising olenes and parains, subjecting at least a portion of said intermediate fraction to a catalytic cracking treatment under conditions to convert a substantial part of the olenes contained therein to lower boiling hydrocarbons while leaving the paraflins in said fraction largely unchanged and returning unconverted paraiiins to the non-catalytic cracking treatment.

3. The process for treating a hydrocarbon distillate containing naphthenes and parafns comprising contacting said distillate oil with a dehydrogenating catalyst at an elevated temperature under time and pressure conditions selectively to dehydrogenate said naphthenes without substantially cracking said distillate and Without substantially converting parafllns to oleflnes thereby converting naphthenes to aromatics and liberating hydrogen, separating the liberated hydrogen from the resultant mixture of aromatics and parafiins, subjecting said mixture to a noncatalytic, vapor-phase cracking treatment under conditions to convert a major portion of the paraiins into light olenes, including oleiines of y 5 and less carbon atoms, said light olenes boilboiling range not exceeding about 50 C.

6.; The process for treating a hydrocarbon distillate containing naphthenes and aliphatics comprising contacting said distillate with a dehydrogenation catalyst at an elevated temperature under time and pressure conditions selectively to dehydrogenate said naphthenes without substantially cracking them. thereby liberating hydrogen, without 4substantially changing the composition of the aliphatics, separating the liberated hydrogen i'romthe resultant mixture ot aromatics and aiiphatics, subjecting the said mixture to a non-catalytic vapor phase cracking treatment under conditions to convert a major portion ofaliphatics into lower boiling hydrocarbons, including olefines or 5 and less carbon atoms, without substantially changing the nuclei of the aromatics, separating from the cracked mixture: an olenic fraction comprising 3 to] 5 carbon hydrocarbons, a tar free aromatic fraction having substantially a boiling range of within that of the original oil. and an intermediate non-aromatic fraction comprising oleiines {and paraiiins, subjecting at least a portion of `said intermediate fraction to a catalytic ARTHUR HALLAM BOULTBEE. 

